Victoria Azarenka of Belarus serves to Daniela Hantuchova of Slovakia during their women's quarter-final match at the U.S. Open tennis championships in New York September 4, 2013. (Photo: Reuters)

Rafael Nadal of Spain looks up at the crowd after defeating compatriot Tommy Robredo following their men's quarter-final match at the U.S. Open tennis championships in New York September 4, 2013. (Photo: Reuters)

Rafael Nadal of Spain celebrates after winning his men's singles quarter final match against Tommy Robredo of Spain on Day Ten of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 4, 2013 in New York City. (Photo: Getty Images)

Rafael Nadal of Spain celebrates after winning his men's singles quarter final match against Tommy Robredo of Spain on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Rafael Nadal of Spain returns a shot to Tommy Robredo of Spain during their men's singles quarter final match on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Rafael Nadal of Spain shakes hands with Tommy Robredo of Spain after their men's singles quarter final match on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Daniela Hantuchova of Slovakia reacts during her women's singles quarter final match against Victoria Azarenka of Belarus on Day Ten of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Victoria Azarenka of Belarus plays a forehand to Daniela Hantuchova of Slovakia during their women's singles quarter final match on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Victoria Azarenka of Belarus celebrates after defeating Daniela Hantuchova of Slovakia in a women's singles quarter final match on Day Ten of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Victoria Azarenka of Belarus and Daniela Hantuchova of Slovakia shake hands after their women's singles quarter final match on Day Ten of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Serena Williams of United States of America plays a backhand next to her partner Venus Williams of the United States of America in action during their women's doubles third round match against Anastasia Pavlyuchenkova of Russia and Lucie Safarova of Czech Republic on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Richard Gasquet of France serves during his men's singles quarter-final match against David Ferrer of Spain on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

David Ferrer of Spain plays a forehand during his men's singles quarter-final match against Richard Gasquet of France on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Richard Gasquet of France shakes hands at the net with David Ferrer of Spain after their men's singles quarter-final match on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Richard Gasquet of France celebrates after defeating David Ferrer of Spain at the U.S. Open tennis championships in New York September 4, 2013. (Photo: Reuters)

Elise Mertens of Belgium in action during her girls' singles second round match against Katie Boulter of Great Britain on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Frederico Ferreira Silva of Portugal serves next to his partner Quentin Halys of France during their boys' doubles second round match against Yoshihito Nishioka of Japan and Jorge Panta of Peru on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Flavia Pennetta of Italy reacts after defeating compatriot Roberta Vinci at the U.S. Open tennis championships in New York September 4, 2013. (Photo: Reuters)

Flavia Pennetta (L) of Italy is congratulated by compatriot Roberta Vinci after her victory at the U.S. Open tennis championships in New York September 4, 2013. (Photo: Reuters)

Flavia Pennetta of Italy serves during her women's singles quarter-final match against Roberta Vinci of Italy on Day Ten of the 2013 US Open at USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)

Daniela Hantuchova

Daniela Hantuchova of Slovakia reacts during her women's singles quarter final match against Victoria Azarenka of Belarus on Day Ten of the 2013 US Open at the USTA Billie Jean King National Tennis Center on September 4, 2013 in the Flushing neighborhood of the Queens borough of New York City. (Photo: Getty Images)